1. Field of the Invention
This invention pertains to improved underground storage tanks principally designed for storage of liquid materials, such as petroleum-based fuels, chemicals and other liquid resources. Specifically, a water-tight riser is provided about a manway, for providing access to the interior of the tank, while maintaining the manway, the riser, an alarm device as provided as well as piping, free of water, drainage, and other liquids that might otherwise accumulate therein.
2. Bacckground of the Prior Art
The use of underground storage tanks for the containment of fluids, such as petroleum fuels and the like, is well known. A typical gasoline service station installation comprises one or more underground storage tanks which can be accessed through a removable plate in the apron of the facility, to fill and remove gasoline. Typically, an underground storage tank is provided with a manway, if large enough to require access to the interior, through which manway a variety of fixtures, such as a filling device, a submersible pump, and other fixtures as required, are provided. While the fixtures generally penetrate through the manway lid, the manway itself may be provided with a removable lid to access the interior of the tank. While other types of underground storage tanks abound and are within the scope of the invention of this application, such as cryogenic tanks and the like, the dominant form of underground storage tank is for the storage of petroleum fuels such as gasoline, diesel fuel and the like.
The initial use of underground storage tanks included the preparation of steel tanks, or tanks of various other metal alloys. Steel, being relatively light weight and sufficiently strong to withstand applied pressures, provide sure resistance and the like, provided a building material which could be easily worked with. Examples of such tanks abound in the literature, and steel tanks are made today for such purposes. One example of early literature directed to steel tanks is U.S. Pat. No. 1,886,074. Steel and other metal alloys are subject to rust and corrosion. Even in a "dry hole," that is an installation provided in the ground which does, not fill with water, rain water, ground water and additional sources of moisture such as runoff and the like, will accumulate and the tank is exposed, both from the inside and the outside, to potential corrosion sources. In the worst case, the hole in which the tank is installed may fill, either due to altered surface circumstances like flooding, leading to an accumulation of water in the hole, or commonly, due to a high water table. Under these circumstances, highly corrosive brine, may be present also in the hole, as is commonly encountered in coastal sites. Corrosion of the tanks can lead to spot holing, as well as weakened strength, buckling and the like. Whether due to holing or a structural collapse, escape of the contained materials from the confines of the tank due to a failure pose severe environmental hazards. Cleanup of released fuel from a failed tank poses severe time and monetary considerations.
To overcome the tendency of steel to rust and corrode, reinforced plastic tanks have been adopted. Specifically, fiberglass reinforced resin tanks have been used, fiberglass tanks being resistant to corrosion and rusting. The resinous material used as the matrix is selected from a variety of materials, specifically desired to be resistant to penetration by, or adsorption of, the fuels or liquids to be contained, including methanol, ethanol as well as more familiar fuels such as gasoline and the like. A wide variety of resins may be employed in a single tank, including a highly specialized coating (such as a vinyl ester resin) to ensure that the contained material cannot pass into the body of the tank, which may be of a more conventional resin. The fiberglass tanks may be molded off of male forms or female forms. Female molding in general gives a more "robust" tank.
Persistent concerns over potential environmental hazards have lead to the adoption of "double-walled tanks," in which the tank containing the fluid material is provided with a surrounding wall, or second wall, such that in the event the interior wall fails, the exterior wall will contain the fluid and avoid release to the environment until repairs can be effected. In the annulus between the inner and outer walls alarm devices of a variety of designs are provided, so as to detect the passage of liquid from the interior tank, or through the exterior tank, into the annulus. In a "dry annulus," detection of the presence of liquid due to changes in sensed electrical conditions are frequently used. A "filled" annulus tank may use an alarm device which senses a change in the fluid level of the annulus, which will occur upon failure of either the inner or the outer tank. In yet a third alternative, the annulus may be slightly pressurized either positively or negatively, such that a leak causes a drop in pressure which may be detected.
In conjunction with such double-walled tanks, it may be customary to provide double-walled piping from the pump, filling means and the like, or in the case of a single network, such as that described in U.S. Pat. No. 4,958,957, piping in and between various tanks. In such a system, the contained liquid is dually contained throughout the system.
In order to access the tank to fill it, to pump fluid out of the tank, to repair the tank and the like, a manway is generally provided into the tank. A releasable cover provided over the manway contains fittings which pass through, and thereby provide a means to pass liquid into and out of the tank. If the tank needs service, and is of a suitable dimension to accommodate a worker, the cover of the manway itself can be removed, to provide access to the interior.
Tanks are generally buried to a standard depth underground. Principal manufacturers of underground storage tanks provide precise instructions as to the depth, size and character of the hole or opening in which the tank will be set. To access the manway from the surface or apron of the installation, it is necessary to have a clear space or column from the manway to the surface. This is provided through a tubular means rising from the surface of the underground storage tank to a point just below the access provided in the ground level of the facility. This device is called a riser.
Frequently piping accessing the manway will go through the riser to the manway. In order to fill the tank, the manway is accessed by opening the cover in the ground level, accessing the manway through the riser, and providing the necessary liquid material. To ensure dual containment of the fluid wherever it passes, the manway itself may be duly contained by the riser. Such a system is described in U.S. Pat. No. 4,958,957. Where the riser is intended as the secondary containment, an alarm means is frequently provided in the riser, to detect the accumulation of liquid therein. For the reasons discussed above, the riser is generally constructed of fiberglass reinforced plastic material, and adhered to the outer wall of the tank, if double walled, by application of resinous material thereto. The riser may be put in place in situ, or provided on the tank.
Recent, repeated severe flooding of many parts of the country has resulted in numerous underground storage tanks where the water level has risen over the top of the riser (indeed, above preexisting ground level) for an extended period of time. Under these circumstances, the cover of the riser, which must be removable to provide access, is lifted by the water and accumulated liquids pour into the riser, frustrating alarm systems, impeding access to the manway, and providing a potential threat to the integrity of dual containment in a double-walled system.
Accordingly, it remains an object of the industry to provide an underground storage tank installation with a riser which provides access to a manway, which riser can be made water-tight and resistant to the penetration of water into the interior of the riser. At the same time, such a water-tight riser must provide easy access to the manway, and if necessary, the interior of the tank.